Means and method for producing wood chips

ABSTRACT

Rotary chipper for producing chips for pulp making is constructed to cause impact of chips from rotary disc cutter at angle such as to cause breakup of cards but minimizing production of pins and fines.

1451 May 9, 1972 United States Patent Smith et a].

[58] FieldofSearch....................24l/l8,28,47,60,92,285. 24l/298; I44/l76, I62

[54] MEANS AND METHOD FOR PRODUCING WOOD CHIPS Q m Q N ha mm Wm mm FC h m m w r w v W c m CV md mm Wm m n e v .m n U UNITED STATES PATENTS Canada 731 Assignee: Rader Pneumatics& Engineering Co. 1.111., 3 2328%; M952 M l't fB b ,(j d unw umclpalyo y am a 685.0!8 10/1901 Unser......1......

July 9,1970

Appl.N0.: 56,173

[22] Filed:

Priman- Emminer-Donhld R. Schran Attorney-Buckhorn. Blore. Klarquist and Spurkman Related U S Appllca on Data R CT commuat'on of Rotary chipper for producing chips for pulp making is conabandoned.

structed to cause impact of chips from rotary disc cutter at angle such as to cause breakup of cards but minimizing production of pins and fines.

[$2] U.S. Cl...................................14l/28, 241/92, l44/l 76,

l44/326 .1527] ll/02 MEANS AND METHOD FOR PRODUCING WOOD CHIPS This application is a continuation of Ser. No. 782,585, filed Dec. 10, 1968, now abandoned.

BACKGROUND OF THE INVENTION In the making of paper pulp from wood by a chemical pulping process, it is desired for several reasons that the wood chips utilized be uniform in size, both in width, length and thickness. To obtain wood chips of the desired size, logs or wood scraps are passed through chippers which comprise rotating discs having radially extending knives which are set to cut off the ends of logs or pieces of wood fed into the cutter so that chips of a predetermined length are formed. The discs on which the knives are mounted are provided with passageways so that the severed chips may pass to the rear of the discs. As chippers have been heretofore constructed, the chips impact with great force against the rear vertical wall of the chipper. One of the undesirable aspects of the chipping process has been the production of slivers or pins, that is, pieces of wood having the desirable length but having a diameter or cross-sectional dimension less than about three-eighths inch, and socalled fines, small sawdust like particles that will pass a threeeighth or one-quarter inch screen. The fines are screened out if the chips are to be used in a chemical pulping process and are discarded and generally simply burned as waste. The fine loss may run between 2% to 6% percent in the ordinary chipping process. The pins are undesirable because some are simply lost in the screening process when they tip on end and pass through the screen which is used to screen out the fines, and in a continuous chemical pulping process because they clog the screen of the digester. In addition, chips are fractured parallel to the grain so that in subsequent handling they break up producing additional fines and pins.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a chipper design which will minimize fracturing of chips and the production of fines and pins.

'Still another object is to provide a chipper design which will provide a more uniform chip size.

Still another object of the invention is to provide a chipper design which will maximize in an off bearing pneumatic conveying system the utilization of the energy imparted to a chip as a result of its severance from a log or piece of wood by the chipping knife.

These and other objects of the invention will become more apparent hereinafter.

We have discovered that fines and pins and fractured chips are produced in a chipper as a result of the impact of the chips upon the rear wall of the chipper at a high incidence angle, and we have further discovered that by reduction of such angle that the percentage of fines and pins produced is markedly reduced. it is highly desirable that some impact take place inasmuch as most chips are removed from a board or log in the form of so-called cards, that is, chunks of wood that are long in the direction transverse to the grain. It is desirable that these cards be broken to some extent and this breakage is conveniently done by impact of the chips as they are projected from the chipper discs.

It is our discovery that if the angle of incidence of the chips upon a surface is controlled so as to be somewhere between about and 35 desirable breakage of the cards will occur with production of a minimum percentage of fines and pins and fractured chips. The optimum angle of incidence will vary depending upon the species of wood, its wetness, the speed of the chipper disc and other factors.

Further details of the invention will be set forth in the following detailed description thereof taken in conjunction with the accompanying drawings.

DRAWINGS FIG. 1 is a semi-schematic plan view, partly broken away, of a chipper constructed in accordance with the invention;

FIG. 2 is a fragmentary section taken generally along line 2-2 of FIG. 1;

FIG. 3 is a side-elevation, partly broken away, of a modified construction in accordance with the invention; and,

FIG. 4 is a semi-schematic side elevation of a chipper constructed in accordance with the prior art.

Referring first to FIGS. 1 and 2, the chipper 10 therein illustrated comprises a chipper disc 12 mounted on the end of a horizontal shaft 14 driven from a suitable motor (not shown) such as through belts l6 and a pulley 18. The disc 12 is contained within a housing 20 which has an opening 22 in its infeed face through which boards or logs may be fed by a horizontal conveyor 24. It will be recognized that many chippers are constructed with an oblique spout inclined at about 45 to the disc through which boards or logs may be fed to the disc and the invention may be utilized equally well with such a chipper feed system.

The chipper disc 12 may be of conventional construction and is provided with a plurality of removably mounted knives 28 which are adapted to sever or slice a predetermined length off a log or piece of board fed into the chipper. The disc 12 is also provided with a plurality of passageways one adjacent each knife through which the severed chips may pass from the front to the back of the disc.

In the conventional chipper, the disc may be driven at a speed of between about 200 to 720 revolutions per minute and the disc may have a diameter of from about 50 to 177 inches. As a consequence, the chips severed by the knives 28 are accelerated to high velocities, for example, as high as to feet per second.

Referring for a moment to FIG. 4, in a typical chipper construction utilized heretofore, chips (represented here by the arrows 38) severed from a log and passing from the disc have impacted upon the conventionally vertical rear wall 40 of the chipper. These chips will have a component of motion inwardly from the circumference towards the center of the disc 12 as well as downward and consequently the actual included angle of impact is somewhat different than is indicated in FIG. 4, but will be of the order of 60. It has been found that it is this high angle of impact that has produced the inordinately high percentage of fines and undesirable slivers or pins and has caused fracturing of chips.

Returning now to FIGS. 1 and 2, it has been our discovery that if the chips which emerge from the cutting disc 12 are directed at an angle of less than 35 upon a surface, the cards of chips will be satisfactorily broken without undue fracturing, and the amount of fines and pins formed will be substantially reduced as compared to the percentage of fines and pins which are produced in a chipper, such as constructed in FIG. 4.

Thus, in accordance with one embodiment of the invention, the chipper is constructed with an impact plate 50 so positioned rearwardly of the cutter disc 12 that the severed chips, indicated at 52, impinge thereupon at an angle of between 5 to 35. The plate 50 has a substantially planar impact section 54 and then curves concavely downwardly towards the bottom of the housing 20 so that the chips can be discharged upon a suitable conveying mechanism, indicated at 58, for removal from the chipper. Any suitable removal system can be utilized. The curved section 56 of the plate 50 serves to suitably reduce the velocity of the chips 52 by reason of the friction of the chips moving along the surface 56 so that further breakage of the chips does not occur.

Preferably the impact plate 50 is mounted in the chipper It] so that the angular relation of the surface 54 to the path of the chips 52 can be adjusted. and thus it is shown in FIG. 2 as supported by a hinge 59. This adjustment is preferred because the desired angle of incidence to obtain the desired breaking up of the cards will vary depending upon the species of wood and the condition of the wood being chipped. in many installations only a single specie of wood may be passed to the chipper, but very frequently it will vary in moisture content. For example, wood cut in the spring of the year and not kept in storage may have a very high sap or moisture content, whereas wood cut in the fall may be relatively dry. It may not be necessary to change the position of the impact plate frequently, but an occasional change may be desired. In any event, it has been found that the angle of incidence desired will generally be about l5 but may vary between 5 and 35.

The surprising reduction in fines and the increased percentage of desirable chip sizes which can be obtained by correct positioning of the impact plate 50 is shown in the table below. This table records the effect of modifying a chipper so as to impact the chips discharged from the cutting disc at an angle of I 5 on an impact plate arranged as shown in FIG. 2, as compared to the previous arrangement of the chipper wherein the chips were impacted at an angle of about 60 on a rear plate such as shown at 40 in FIG. 4. The chipper upon which these tests were performed had a 66-inch cutter disc with gravity infeed and bottom discharge. The disc was driven at 720 RPM. "Test 1'' indicates results with conventional chipper, Test 2 indicates results after placement of an impact plate in accordance with the invention.

TABLE-RESULTS FROM CHANGE OF IMPACT ANGLE Screen size of chips, inches Because of the problems it creates in a continuous chemical digesting process such as the Kamyr, it is often necessary to discard all or a substantial part of the material passing through a three-eighth inch screen. What fines are used reduce pulp quality in a continuous process and also in a batch process. It will be observed that by utilizing an impact plate in accordance with the invention, the fines as a result of chipping fir are reduced by 50 percent from a total of 7. l percent to 3.49 percent ofthe chips.

Furthermore, the percentage of chips falling in the most desirable range, that is, from one and one-quarter inch to onehalf inch, was increased from 7 l .0 percent to 81.4 percent.

Likewise, in the case of hemlock, the amount of fines was reduced from 6.59 percent to 4.72 percent, whereas the percentage of chips in the most desirable range was increased from 73.6 percent to 81.1 percent.

While the savings in the amount of rejected material may sound small as being only of the range of two to three percent, when it is realized that the pulp presently produced annually within the United States by chemical processes has an estimated value of over billion dollars it can be seen that these percentages represent a very substantial monetary value.

Referring now to FIG. 3, there is shown therein a modified housing arrangement for passing the chips directly into a pneumatic conveying system. The chipper 60 illustrated in FIG. 3, is provided with a disc 12 identical to that shown in FIG. I, and is fed horizontally by a conveyor 24. However, the chipper 60 is provided with an impact plate 62 upon which the chips 52 impinge and are guided thereby into the entry section 64 of a pneumatic conveying system. Chips discharging from a rotor of 66 inch diameter and driven at a speed of 720 RPM can have a velocity of about 165 feet per second whereas in the conventional pneumatic system the air velocity therethrough is of the order of B0 to l feet per second. It is desirable to utilize as much of the energy in the chips for conveying as is possible consistent with the desire to prevent excessive breakage of the chips. Accordingly, plate 62 is inclined at the optimum angle to obtain breakage of cards without producing fines and pins, and so that chips passed through the entry section 64 to the conveying system will have a velocity equal to or higher than the air in the conveying system so that their energy is utilized efficiently. Again, it is preferable that the impact plate 62 be mounted so that its position may be adjusted to receive the chips at an impact angle which will give optimum card breakage with minimum production of fines depending upon the species and its condition. Accordingly, the impact plate 62 is shown as supported on a hinge 66 to permit a change of angle thereof with respect to the path of the chips 52. A sliding plate 68 may be provided on the housing to adjust for the position of the upper portion of the chip guiding section 64 as the position of the impact plate 62 is changed.

Having illustrated and described a preferred embodiment of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. We claim all such modifications as come within the true spirit and scope of the appended claims.

We claim:

l. in a wood chipper comprising a rotary disc having a plurality of radially extending knives along one face of said disc for cutting chips from lengths of wood fed toward said face from which knives the chips are propelled at high velocities along a predetermined path, and a plurality of radially extending passageways one adjacent each knife for permitting the severed chips to pass through the disc,

conveying means for receiving such chips and conveying them away from said chipper,

and impact means positioned between said disc and said conveying means having an impact surface for receiving said chips,

said impact surface extending at an angle of between about five and thirtyfive degrees to said predetermined chip path.

2. A chipper as set forth in claim 1 including means mounting said impact means to permit adjustment of the angle of said impact surface relative to said predetermined path.

3. A chipper as set forth in claim I,

said impact means comprising a plate having a substantially planar impact surface portion and a merging concave surface for receiving chips from said planar surface portion.

4. A chipper as set forth in claim 1 wherein said impact surface extends at an angle of about fifteen degrees to said predetermined chip path.

5. A method of preparing wood chips for the making of pulp which comprises:

feeding a piece of wood to a rotary disc chipper so as to slice lengths of predetermined amount from the end of said piece and crosswise of the grain thereof,

causing the lengths so cut to impinge upon a first surface inclined at an angle of between 5 and 35 to the path of travel of said chips as they emerge from said disc,

and thereafter retarding the speed of said chips before permitting further impact of said chips upon a further surface.

6. The method of claim 5 wherein the chips are passed from said first surface onto a concavely curved surface so as to reduce the velocity of said chips and minimize breakage thereof.

7. A method of preparing wood chips for the making of pulp which comprises:

feeding a piece of wood generally perpendicularly to a high speed rotary disc chipper so as to slice crosswise of the grain chips of predetermined length from the end of said piece,

and causing the chips so cut to impinge upon a surface inclined at an acute angle of less than about 35 to the path of travel of said chips as they emerge from said disc, thereby minimizing breakage of said chips.

8. A method as set forth in claim 7 wherein said acute angle is between about 5 and 35.

9. A method as set forth in claim 7 wherein said acute angle is l5.

10. The wood chipper of claim 1 wherein said means comprises pneumatic conveyor means.

H. The wood chipper of claim 7 wherein said pneumatic conveyor means creates a stream of air having a direction conveying component parallel to said path for carrying the chips away from said chipper.

i k I 

2. A chipper as set forth in claim 1 including means mounting said impact means to permit adjustment of the angle of said impact surface relative to said predetermined path.
 3. A chipper as set forth in claim 1, said impact means comprising a plate having a substantially planar impact surface portion and a merging concave surface for receiving chips from said planar surface portion.
 4. A chipper as set forth in claim 1 wherein said impact surface extends at an angle of about fifteen degrees to said predetermined chip path.
 5. A method of preparing wood chips for the making of pulp which comprises: feeding a piece of wood to a rotary disc chipper so as to slice lengths of predetermined amount from the end of said piece and crosswise of the grain thereof, causing the lengths so cut to impinge upon a first surface inclined at an angle of between 5 and 35* to the path of travel of said chips as they emerge from said disc, and thereafter retarding the speed of said chips before permitting further impact of said chips upon a further surface.
 6. The method of claim 5 wherein the chips are passed from said first surface onto a concavely curved surface so as to reduce the velocity of said chips and minimize breakage thereof.
 7. A method of preparing wood chips for the making of pulp which comprises: feeding a piece of wood generally perpendicularly to a high speed rotary disc chipper so as to Slice crosswise of the grain chips of predetermined length from the end of said piece, and causing the chips so cut to impinge upon a surface inclined at an acute angle of less than about 35* to the path of travel of said chips as they emerge from said disc, thereby minimizing breakage of said chips.
 8. A method as set forth in claim 7 wherein said acute angle is between about 5* and 35*.
 9. A method as set forth in claim 7 wherein said acute angle is 15*.
 10. The wood chipper of claim 1 wherein said conveying means comprises pneumatic conveyor means.
 11. The wood chipper of claim 7 wherein said pneumatic conveyor means creates a stream of air having a direction component parallel to said path for carrying the chips away from said chipper. 